Pyrrolidone polymerization catalyst system

ABSTRACT

The process of making a catalyst for the polymerization of 2-pyrrolidone by contacting an alkali metal pyrrolidonate, a quaternary ammonium carboxylate and carbon dioxide.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 724,801, filedSept. 20, 1976, now U.S. Pat. No. 4,101,447.

BACKGROUND OF THE INVENTION

Poly-2-pyrrolidone is produced by the alkaline-catalyzed polymerizationof 2-pyrrolidone. The catalyst system may comprise a partiallycarbonated pyrrolidonate salt made, for example, by reacting an alkalimetal hydroxide with 2-pyrrolidone, or by reacting a quaternary ammoniumhydroxide with 2-pyrrolidone, dehydrating, and contacting the productwith carbon dioxide (U.S. Pat. No. 3,721,652). Japanese Pat. No.47-26195 discloses a process for making a catalyst by reacting anon-water-forming alkali metal compound with 2-pyrrolidone andcontacting the product with a quaternary ammonium halide under anhydrousconditions. For many purposes, it is advantageous to be able to rapidlyproduce poly-2-pyrrolidone having high molecular weight, e.g. in excessof 500,000, in good yield.

BRIEF SUMMARY OF THE INVENTION

A catalyst, capable of producing a high molecular weightpoly-2-pyrrolidone is made by contacting an alkali metal pyrrolidonate,certain quarternary ammonium carboxylates and carbon dioxide.

DESCRIPTION OF PREFERRED EMBODIMENTS

The catalyst of the present invention is capable of producingpoly-2-pyrrolidone of weight average molecular weight in excess of500,000. The present catalyst also achieves high yields and highconversion rates without diminution of molecular weight. The catalystdoes not require an anhydrous source of alkali metal pyrrolidonate andit is preferred to certain other onium salt catalysts for its solubilityin the 2-pyrrolidone polymerizate.

Catalyst System

In the process of the present invention a catalyst for thepolymerization of 2-pyrrolidone is made by contacting an alkali metalpyrrolidonate, certain quaternary ammonium carboxylates and carbondioxide in mol ratio of about 1:0.1-2:0.1-0.5, preferably in mol ratioof about 1:0.2-1.5:0.1-0.5, and most preferably in a mol ratio of about1:1:0.3.

The reactants, i.e. the pyrrolidonate, the ammonium carboxylate and thecarbon dioxide, may be contacted in any order beginning with thepyrrolidonate as one of the components. It is preferred, but notnecessary, to add the quaternary ammonium carboxylate to the previouslycarbonated pyrrolidonate salt. In a preferred embodiment, the catalystof the present invention is formed in a solution of 2-pyrrolidone. Analkali metal hydroxide is added to an excess of 2-pyrrolidone, withwhich it reacts to produce a solution of the alkali metal pyrrolidonateand water in 2-pyrrolidone. The solution is dehydrated until it containsless than about 0.1-0.2 weight percent water. Then carbon dioxide isadded in the desired mol ratio to the pyrrolidonate in the solution at atemperature of about 25°-30° C. The quaternary ammonium carboxylate isalso added in the desired mol ratio to the pyrrolidonate at about thesame temperature.

The preferred quaternary ammonium carboxylate of the present inventionis a lower alkyl tetraalkyl ammonium carboxylate of a lower alkanoicacid. The tetraalkyl ammonium carboxylate may be produced by theneutralization of the carboxylic acid with a tetraalkyl ammoniumhydroxide. The tetraalkyl ammonium carboxylate is preferably a tetra(C₁-C₆)alkyl ammonium carboxylate, and more preferably a tetra(C₁ -C₃)alkylammonium carboxylate. Representative alkyl groups include methyl, ethyl,propyl, isopropyl, butyl, isobutyl, t-butyl, hexyl, etc. The carboxylateis preferably the alkanoate of a C₁ -C₆ alkanoic acid, more preferably aC₁ -C₃ alkanoic acid and most preferably, the acetate. Representativetetraalkyl ammonium carboxylates include tetramethyl ammonium acetate,tetraethyl ammonium acetate, dimethyldiethyl ammonium propionate, etc.The ammonium carboxylate may be used as a combination of species, e.g.as a mixture of tetramethyl ammonium acetate and tetraethyl ammoniumacetate. However, the ammonium carboxylate should be substantiallysoluble under the alkaline conditions of catalyst system preparation andpolymerization in order to show an appreciable effect on thepolymerization reaction. In this regard, tetramethyl ammonium acetateshows a considerable advantage over the corresponding halide,tetramethyl ammonium chloride, since it is much more soluble in thepolymerizate.

The alkali metal pyrrolidonate is preferably sodium or potassiumpyrrolidonate. For certain purposes, it may be advantageous tosubstitute for pyrrolidonate in whole or in part an alkali metalcaprolactamate or the alkali metal salt of another low-molecular-weightlactam, but this is normally not preferred to the use of thepyrrolidonate. The alkali metal pyrrolidonate is preferably made bycontacting the alkali metal hydroxide with excess 2-pyrrolidone, butother methods may be chosen, such as by reacting 2-pyrrolidone with analkali metal or an alkali metal alkoxide. While it is preferable tocontact the tetraalkyl ammonium carboxylate, the pyrrolidonate andcarbon dioxide in a 2-pyrrolidone solution, inert solvents may be usedin whole or in part to replace the 2-pyrrolidone. Sulfur dioxide isbelieved to be a partial substitute for carbon dioxide, and its use isnot barred in the practice of the present invention.

In the catalyst system of the present invention, polymerizationinitiators and polymerization accelerators may also be used.Unexpectedly rapid polymerization to poly-2-pyrrolidone ofsatisfactorily high molecular weight is achieved in this catalyst systemby the addition of 0.05-1.5 mol percent of acetic anhydride. Preferably0.05-1.0 and most preferably about 0.05-0.5 mol percent of aceticanhydride is used. Suitable accelerators are also described in U.S. Pat.No. 3,721,652 and include N-acyl lactam, particularly the N-acylpyrrolidones, preferably N-acetyl pyrrolidone.1-(1-pyrrolin-2-yl)-2-pyrrolidone is a particularly preferred activator.

Polymerization Conditions

The polymerization process of this invention is specifically applicableto the polymerization of 2-pyrrolidone to form a polymeric carbonamideof high molecular weight in a reasonably short polymerization time, forthis reaction, of 4-24 hours. The high-molecular-weight polymer iscapable of being formed into filaments having substantial orientationalong the filamentary axis, high tensile strength and other propertiessuitable for making into textiles. It can be made into shaped articlesand film by melt-molding or extrusion.

In order to produce high-quality poly-2-pyrrolidone capable of beingformed into fibers, filaments and yarn of commercial textile quality, itis necessary that the 2-pyrrolidone be of high purity. Depending uponthe process of manufacture, commercially available 2-pyrrolidone maycontain appreciable amounts of various impurities, some of which arebelieved to interfere deleteriously with polymerization. Purification ofthe monomer to polymerization grade is achieved by known purificationtechniques, including distillation.

The process of the present invention is applicable to the production ofpolymers of C-alkyl-substituted pyrrolidone, such as4-methyl-2-pyrrolidone and copolymers of 2-pyrrolidone, such as withcaprolactam, as well as to the production of poly-2-pyrrolidone.Consequently, in general, and unless otherwise indicated, "monomer"denotes 2-pyrrolidone, substituted 2-pyrrolidone, and any compoundcapable of copolymerizing with 2-pyrrolidone under the stated conditionsof alkaline polymerization catalysis.

Preferably, the catalyst system comprises about 0.5-30 mol percent ormore of the 2-pyrrolidone-catalyst mixture, based on total2-pyrrolidone, more preferably about 5-20 mol percent, and mostpreferably about 10 mol percent catalyst. Total 2-pyrrolidone consistsof 2-pyrrolidonate catalyst, including alkali metal pyrrolidonate andquaternary ammonium pyrrolidonate, as well as carbonated alkali metalpyrrolidone and carbonated quaternary ammonium pyrrolidonate, and2-pyrrolidone provided as solvent to said catalyst, and any additionalmonomer charged to the mixture for polymerization reaction. Thepolymerization catalyst system is believed to principally comprisequaternary ammonium pyrrolidonate and carbonated quaternary ammoniumpyrrolidonate, but substantial amounts of alkali metal pyrrolidonate andcarbonated alkali metal pyrrolidonate (carboxypyrrolidonate) may also bepresent, depending upon the mol ratios chosen. Alkali metal carboxylateis thought to be present, but it is believed to be inert towards thepolymerization reaction.

In general, 2-pyrrolidone may be polymerized at a temperature from about15° C. to about 100° C., preferably 25° C. to 70° C., and mostpreferably from about 40° C. to about 60° C., under a pressure rangingfrom subatmospheric to superatmospheric, in the presence of the catalystsystem for a period from about 4 to about 100 hours or longer,preferably for about 8 to about 72 hours, and most preferably from about8 to about 48 hours. In continuous operation, polymerization time refersto average residence under polymerization conditions. A small amount ofwater, not exceeding about 0.1-0.2 weight percent, based on total2-pyrrolidone, is permissible in the reaction mixture, but less then 0.1weight percent is preferred.

Preparation of polymers of 2-pyrrolidone, according to the normalprocess of this invention, can be carried out with various amounts ofmonomers, catalyst, inert nonsolvent liquids, initiators and otheradditives--the amount of each being properly coordinated to produce themost effective polymerization--with or without stirred reactors, by bulkpolymerization, solution polymerization, or otherwise, continuously orbatchwise. Although the preferred conditions and amounts of thecomponents in the reaction have been given, it is understood that theseare not intended to be limitations to polymerization, since it may bepossible to achieve substantial polymerization outside the preferredranges.

EXEMPLIFICATION Example 1

200 g of purified 2-pyrrolidone (2.3 mols) was contacted with 7.7 g ofKOH pellets (0.117 mol, 85.5% KOH) in a stirred reactor vessel and themixture heated to incipient distillation under reduced pressure at atemperature of about 115° C. The mixture was cooled and a calibratedamount of carbon dioxide was introduced to produce a polymerizatecontaining 30 mol percent carbon dioxide based on potassium. About 10 gof the polymerizate was poured into each of several successivepolyethylene bottles, three of which contained 6 millimols of the driedonium salts shown in Table I. The bottles were shaken well and held at50° C. for 22 hours. The polymer was then removed, washed, dried andweighed. The molecular weight was determined as described elsewhere. Theresults are given in Table I.

Example 2

The process of the present invention was tested in another exampleotherwise duplicative of Example 1. 50 g of purified 2-pyrrolidone wascontacted with 1.93 g of KOH pellets (85.5% KOH) in a stirred reactionvessel and the mixture was heated to incipient distillation underreduced pressure at a temperature of about 110° C. The mixture wascooled and a calibrated amount of carbon dioxide was introduced toproduce a polymerizate comprising 30 mol percent carbon dioxide based onpotassium. 1.5 millimols of the previously dried tetramethylammoniumacetate was weighed into a polyethylene bottle and 10 g of polymerizatewas added to it. The bottle was shaken well and polymerized at 50° C.for 22 hours. The product was worked up as described in Example 1. Theresults are given in Table I.

                                      TABLE I                                     __________________________________________________________________________    Comparative Polymerization Results.sup.1                                                        Mol Ratio                                                                             Percent                                             Onium Salt        K/Onium Salt                                                                          Conversion                                                                          Mw × 10.sup.-3                          __________________________________________________________________________    Example 1                                                                           None        --      37    405                                           Example 2                                                                           (CH.sub.3).sub.4 N + OCOCH.sub.3.sup.-                                                    1.2     56    720                                           Example 1                                                                           (CH.sub.3).sub.4 N + ClO.sub.4.sup.-                                                      1       31    400                                           Example 1                                                                           (CH.sub.3).sub.4 N + bf.sub.4                                                             1.1     35    415                                           Example 1                                                                           (CH.sub.3).sub.4 n + PF.sub.6.sup.-                                                       1       33    405                                           __________________________________________________________________________     .sup.1 50 mol percent potassium pyrrolidonate from KOH.                       30 mol percent CO.sub.2 based on K.                                           Polymerized 22 hours at 50° C.                                    

Table I shows comparative polymerizations in the presence of potassiumpyrrolidonate and carbon dioxide with and without tetramethyl ammoniumacetate. The tetraalkyl ammonium carboxylate in combination with carbondioxide and potassium pyrrolidonate is found to be capable of producingpolypyrrolidone of extremely high weight average molecular weight. Allmolecular weights are reported as the weight average molecular weightdetermined from the specific viscosity of 0.1 gram of polymer/100 cc ofm-cresol solution at 25° C. All reported percentages are mol percentunless otherwise indicated. Percent conversion is calculated as100x(weight of polymer)/(weight of total 2-pyrrolidone) and total2-pyrrolidone has been heretofore defined.

What is claimed is:
 1. A process for polymerizing 2-pyrrolidone, to forma polymer product capable of being formed into filaments, shape articlesor films, which comprises polymerizing 2-pyrrolidone in the presence ofa catalyst system consisting essentially of an alkali metalpyrrolidonate, quaternary ammonium carboxylate, and carbon dioxide in amol ratio of about 1:0.1-2:0.1-0.5.
 2. The process of claim 1 whereinsaid catalyst system is prepared by first contacting said alkalipyrrolidonate with carbon dioxide to form a carbonated pyrrolidonatesalt and then contacting said carbonated pyrrolidonate salt with saidquaternary ammonium carboxylate.
 3. The process of claim 1 wherein saidquaternary ammonium carboxylate is a tetraalkyl ammonium carboxylate. 4.The process of claim 3, wherein the carboxylate moiety of saidtetraalkyl ammonium carboxylate is an alkanoate of a C₁ -C₆ alkanoicacid.
 5. The process of claim 4, wherein said tetraalkyl ammoniumcarboxylate is a tetraalkyl ammonium acetate.